In the past two decades, innovations in the diagnosis of cardiovascular disease have expanded from external imaging processes to internal, catheterization-based, diagnostic processes. Diagnosis of cardiovascular disease has been performed through angiogram imaging wherein a radiopaque dye is injected into a vasculature and a live x-ray image is taken of the portions of the cardiovascular system of interest. More recently, however, diagnostic equipment and processes have been developed for diagnosing vasculature blockages and other vasculature disease by means of ultra-miniature sensors placed upon a distal end of a flexible elongate member such as a catheter, or a guidewire used for catheterization procedures.
One such ultra-miniature sensor device is a pressure sensor mounted upon the distal end of a guidewire. A particular example of such a pressure sensor is provided in Corl et al. U.S. Pat. No. 6,106,476, the teachings of which are expressly incorporated herein by reference in their entirety. The intravascular pressure sensor measures blood pressure at various points within a vasculature and facilitates locating and determining the severity of stenoses or other disruptors of blood flow within blood vessels. Such devices are commonly used to determine the effectiveness of an angioplasty procedure by placing the pressure sensor distal to a stenosis and measuring a pressure difference relative to the proximal pressure measured through a guiding catheter by traditional methods. A significant pressure gradient, for example greater than 30 mmHg, is indicative of a functionally significant blockage of the vessel.
A presently used manufacturing technique for manufacturing a solid-state pressure sensor for an intravascular pressure sensor wire relies upon a mechanical saw to shape the pressure sensor. In the known mechanically shaped devices, wafer thinning is an important step in fabricating a solid-state pressure sensor chip. Normally, pressure sensors are fabricated on or near a surface of a relatively thick supporting wafer of either silicon or glass. The supporting wafers are typically 400 μm or more in thickness, and the supporting wafers are robust and suitable for manual handling or handling by automated fabrication machinery. However, at a latter stage of the production process, it is necessary to thin the wafer to less than 100 μm, possibly as thin as 50 μm, to produce a device mountable within a coronary guidewire. The thin wafer is difficult to handle and subject to breakage or other damage in subsequent processing steps such as diamond saw dicing which cuts the wafer into tiny rectangular sensor chips that can be subsequently mounted in a guidewire.
The known fabrication process for pressure sensors using diamond saw dicing is fast, efficient, and therefore widely used. However, the diamond sawing is only capable of rendering simple “rectangular” device outlines.
Once the pressure sensor is mounted in a guidewire or similar device, it is subject to external stress arising from bending of the guidewire to access the coronary anatomy, or from differential thermal expansion of the various guidewire components. External stress on the pressure sensitive portion of the sensor chip can produce undesirable pressure artifacts. A guidewire containing a pressure sensor includes a housing that facilitates cantilever mounting of the sensor chip. The cantilever mounting arrangement ensures that surrounding guidewire structures do not exert external stress to the pressure sensitive region of the chip.
Deep reactive-ion etching (DRIE) is a highly anisotropic etch process for creating deep, steep-sided holes and trenches in solid-state device wafers, with aspect ratios of 20:1 or more. DRIE was originally developed for microelectromechanical systems (MEMS). However, DRIE is also used for producing other devices such as to excavate trenches for high-density capacitors for DRAM. DRIE is capable of fabricating 90° (truly vertical) walls.